Lotus Elan

differential problem (maybe?)

PostPost by: peg_pilot » Sat Nov 19, 2005 4:54 pm

I am having some strange (to me) vibration problems with my diff.
When the car has been driven enough to warm up thoroughly, and ONLY
when it is thoroughly warm, I start getting very noticeable
vibrations from the back end when I turn. It feels like the diff is
alternately sticking and slipping, almost as if it had a series of
detents in the side gears (I don't mean that I literally think there
are detents in there, but it feels like it). Is this what a limited-
slip differential feels like ? There are other performance parts on
the car (71 Series 4 FHC) that were put on by a previous owner, so it
is not impossible that one was fitted.
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PostPost by: "e s" » Sat Nov 19, 2005 5:49 pm


wheel bearings

diff bearings

axle shaft wear

upper diff mounts

Crawl under start banging around
"e s"

PostPost by: "Sean Murray" » Sat Nov 19, 2005 9:49 pm

Hi Peg-pilot

It is possible that while your crown wheel and pinion are fine, the actual differential gears might be in trouble, or you may have a LSD.

Try jacking up one rear wheel and turning the wheel by hand, with neutral selected, . A normal differential should turn the propshaft with little effort, a LSD will need much greater effort, and any roughness will indicate a differential-ectomy

Sean Murray
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PostPost by: poiuyt » Sun Nov 20, 2005 5:06 am

A friend of mine in the late 1960s installed a Detroit Locker limited
slip in his Daysun 2000 roadster and it worked just like you describe.
May or may not be a limited slip in your car.

Steve B.<br>1969 Elan S4
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PostPost by: Rob_LaMoreaux » Sun Nov 20, 2005 11:39 am

I have an LSD installed on my car and it feels similar at times. As it has
loosened up it has gotten better.

Someone already described how to tell if an LSD is installed to try that to

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PostPost by: lotuselan2 » Mon Nov 21, 2005 9:24 pm

Some LSD's tend to lock up when quite hot; then you have a "locker". My
Vauxhall Firenza racer did that. It should only vibrate when cornering at
low speed; it is then actually wheel hop that you would feel. If someone is
watching the car it would be obvious looking at the rear wheels. It should
run and sound smooth at in a straight line.


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'69 Lotus Elan +2 with Cosworth BDR
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PostPost by: "denicholls2" » Fri Dec 02, 2005 12:26 am

A much less subjective test for the presence of an LSD hasn't been
mentioned. Get both rear wheels off the ground, and with the car in
gear turn one.

If the opposite side turns the OPPOSITE direction, you have an open
diff. And from the sounds of it, a rebuild in your future.

If the opposite side turns the SAME direction, you have an LSD. This
is caused by the clutches that attempt to simultaneously turn both
wheels under all conditions except hard cornering.

The drag mentioned here in the "one wheel up" test will also be
present, but problems in the driveline can also cause drag, so its
presence does not by itself certify you have an LSD.

Doug Nicholls, 54/1822 Ma~

PostPost by: "Sean Murray" » Fri Dec 02, 2005 1:48 am

Agree with you there Doug, I omitted to mention this obvious check..

Sean Murray
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